Present methods of forming an implantation space between adjacent vertebral bodies in the human spine generally include the use of one or more of the following: hand held biting and grasping instruments known as rongeurs; curettes; drills and drill guides; rotating burrs driven by a motor; and osteotomes and chisels. Sometimes the vertebral end plate must be sacrificed as occurs when a drill is used to drill across the disc space and deeper into the vertebral bodies than the thickness of the bony end plate region. Such a surgical procedure necessarily results in the loss of the hardest and strongest bone tissue of the vertebral bodies located in the bony end plate region and thereby removes from the vertebral bodies that portion of its structure best suited to absorbing and supporting the loads placed on those vertebral bodies by an interbody spinal implant. Nevertheless, the surgeon must work upon the adjacent end plates of the adjacent vertebral bodies to access the underlying vascular bone that is capable of participating in the fusion by allowing active bone growth, and also to attempt to obtain an appropriately shaped surface in the vertebral bodies to receive the implant. Because the end plates of the adjacent vertebral bodies are not flat, but rather have a compound curved shape, and because the implants, whether made of bone or any other suitable implant material, when fabricated or manufactured, tend to have a geometric rather than a biologic shape, it is generally necessary to conform at least a portion of the vertebral bodies to the shape of the implant to be received therebetween.
It is important in forming the space between the adjacent bone structures to provide a surface contour that closely matches the contour of the implants so as to provide an adequate support surface across which the load transfer between the adjacent bone structures can be evenly applied. In instances where the surgeon has not been able to form the appropriately shaped space for receiving the implants, those implants may slip or be forcefully ejected from the space between the adjacent vertebral bodies, or lacking broad contact between the implant and the vertebral bodies, a failure to obtain fusion may occur.
Prior devices having a plurality of rotating cutting elements for removing bone with a drive mechanism between the cutting elements had limitations in certain applications. For example, if the bone to be cut was thicker than the individual thickness of each of the cutting elements, then the portion of the device between the cutting elements could hit the uncut bone and stop the bone removal device from advancing deeper into the bone being cut. Further, the presence of the drive member between the cutting elements kept the cutting elements spaced apart and thus could prevent the placement of the bone removal device into very narrow spaces such as, but not limited to, disc spaces as might be found in some instances in the cervical spine.
There remains therefore a need for an improved spinal interspace shaper that does not have such limitations so as to achieve the desired purposes as described herein.